[Bug lto/82575] New: [8 Regression] lto debugobj references __gnu_lto_slim, ld test liblto-17 fails

[amodra at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82575

            Bug ID: 82575
           Summary: [8 Regression] lto debugobj references __gnu_lto_slim,
                    ld test liblto-17 fails
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amodra at gmail dot com
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---
           Summary: [8 Regression] lto debugobj references __gnu_lto_slim,
                    ld test liblto-17 fails

I recently upgraded the set of cross-compilers I use to test binutils, and
found that gcc trunk causes fails of some ld lto tests.

+FAIL: Build liblto-17a.so
+FAIL: Build liblto-17b.so 1
+FAIL: Build liblto-17b.so 2

Seen on aarch64-linux, arm-linuxeabi, hppa-linux, m68k-linux, mips64-linux,
nios2-linux, powerpc64le-linux, powerpc64-linux, powerpc-linux, s390-linux,
s390x-linux, sparc64-linux, tilepro-linux, and x86_64-linux.

Breakpoint 3, elf_link_add_object_symbols (info=<optimised out>, abfd=0xa6d1c0)
at /home/alan/src/binutils-gdb/bfd/elflink.c:4336
4336          if (isym->st_shndx == SHN_COMMON
(gdb) p name
$8 = 0xa70cd3 "__gnu_lto_slim"
(gdb) p abfd->filename
$9 = 0xa6d100 "/tmp/ccF0RcA1debugobj"

The debugobj is from
powerpc64le-linux-gcc -B /home/alan/build/gas/powerpc64le-linux/ld/tmpdir/ld/
-mcpu=power8 -r -nostdlib -o /tmp/ccF0RcA1debugobj /tmp/ccuOMpMydebugobjtem
[Leaving LTRANS /tmp/ccuOMpMydebugobjtem]

$ readelf -s --wide /tmp/ccF0RcA1debugobj
Symbol table '.symtab' contains 8 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND 
     1: 0000000000000000     0 SECTION LOCAL  DEFAULT    1 
     2: 0000000000000000     0 SECTION LOCAL  DEFAULT    3 
     3: 0000000000000000     0 SECTION LOCAL  DEFAULT    4 
     4: 0000000000000000     0 FILE    LOCAL  DEFAULT  ABS lto-17a.c
     5: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND __gnu_lto_slim
     6: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND __gnu_lto_v1
     7: 0000000000000000     0 NOTYPE  WEAK   HIDDEN     1 lto_17a.c.4af7515b

$ readelf -s --wide /tmp/ccuOMpMydebugobjtem
...
    22: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND __gnu_lto_v1
    23: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND __gnu_lto_slim

These references in LTO *output* files result in __gnu_lto_slim appearing as a
dynamic symbol in liblto-17a.so and liblto-17b.so.  nm doesn't like that, and
you get a complaint about missing plugins.  I don't believe the linker is doing
anything wrong here..